The project is designed to develop new instrumentation and methodology or improve existing instrumentation and methodology for characterization of biological macromolecules and for studying their interactions. Analytical ultracentrifugation, the techniques ancillary to it, and methods of data analysis using mathematical modeling appropriate for these techniques are the major areas of interest. The major emphasis in this project has been given to the development of new applications of the techniques of mathematical modeling to problems in ultracentrifugal analysis. The two areas this project has been concerned with have been an extension of the method of implicit constraints to a wider range of studies of macromolecular interactions and a new approach toward obtaining molecular weight distributions in solutions of macromolecular biopolymers. MLAB, operating on the DEC-10 computer, has been used for the mathematical modeling. The applications of these studies are described in the annual report entitled Physical Chemistry of Biological Macromolecules. No new work on data acquisition has been carried out except for the continuation of a study on the possibility of development of new optical data acquisition systems for the conversion of curent preparative ultracentrifuges into analytical ultracentrifuges with superior capabilities as analytical instruments at a fraction of the cost of the current instruments. New preliminary designs for such systems have been developed.